New Design Yields Higher Torque Efficiency

Designers of skid-steer loaders may now have an alternative to the cam lobe-type hydraulic motors typically used to propel the wheels in such equipment.

Thanks to a new design, less costly orbital motors might now be able to provide the high torque efficiency and longer bearing life needed for such applications. The new design, developed by engineers at Sauer-Danfoss Inc. (Nordborg, Denmark), also enables orbital motors to operate at higher pressures than was previously possible.

"We are closer to the performance of the cam lobe motor than we are to the conventional geroler (orbital motor)," notes Jeff Brenner, product manager for low-speed, high-torque motors at Sauer-Danfoss.

By improving the performance of conventional orbital motors, Sauer-Danfoss engineers believe they have created a new niche—one that exists in a gap that lies between the conventional geroler-type motor and the more costly cam lobe motor.

"In the past, there were a lot of applications in which the designer had no choice but to pass up the orbital motor and go to the cam lobe," Brenner says.

Among those applications were skid-steer loaders, forestry equipment, rough terrain scissors lifts, asphalt pavers, and heavy duty lawn and turf vehicles. For many of those vehicles, conventional orbital motors lacked the torque efficiency and bearing life needed to stand up to the demanding duty cycles. The reason, at least in part, was the inability of orbital motors to operate at higher pressures. In contrast, many cam lobe motors could operate at pressures exceeding 5,000 psi for extended periods. As a result, engineers were willing to pay a cost penalty—sometimes as much as 40 percent—to get them.

Sauer-Danfoss' new T-series of orbital motors, however, could change all that. The company's engineers won't discuss how they've boosted the pressure capacities of the new line of motors, but they will say that the motors are rated at 3,650 psi (250 bar) for continuous and 5,075 psi for intermittent pressure, which is significantly higher than conventional orbital motors. The largest motor frame in the T-series line also offers displacements ranging from 400 to 800 cc, making it capable of heavy-duty propulsion and work functions.

Equally important, the company says that the additional performance capability has come without an associated heat increase. The company's engineers say that the extra torque is achieved "without wasting horsepower," which in turn means that machine designers needn't be concerned about the extra space required for larger cooling systems.

"If you have better efficiency, the machine designer has less horsepower that needs to be cooled," Brenner says. "And for a skid-steer loader, that's a major advantage."

Sauer-Danfoss says that T-series is making its initial impact in the design
of several unnamed skid-steer loaders. The company's engineers expect, however,
that the T-series will ultimately have a broader impact, providing capabilities
for other vehicles, particularly in forestry. There, they say, it could find a
place in so-called "harvester heads." It could also carve out a niche in
skid-steer attachments, such as sweepers and trenchers, which require high
pressure for simultaneous lifting and pushing motions.

"This technology is going to take a bite out of the existing cam lobe market and geroler market," Brenner notes. "The machines being designed today are getting more powerful and heavier. They need higher pressure and greater productivity."

Focus on Fundamentals consists of 45-minute on-line classes that cover a host of technologies. You learn without leaving the comfort of your desk. All classes are taught by subject-matter experts and all are archived. So if you can't attend live, attend at your convenience.